the COUNTRIES array in uloc.c and the tempCountries array in ULocale.java do not contain the country code "RS" for Serbia. Also, the country code "CS" should be deprecated and mapped to "RS".
Basically, the lists are out of sync. with CLDR.
Also, TestISOFunctions in cloctst.c should test the countries as well as the languages. (And, I presume, the matching test in ICU4J?)